Drunk driving of a vehicle (for example, automobile) is now a serious social problem. A driver is therefore strictly prohibited from driving a vehicle under the influence of alcohol drinking. However it all depends on a driver whether he or she refrains from driving a vehicle after drinking alcohol. JP 2005-224319A proposes technology, which forcibly restrains a driver under the influence of alcohol drinking from driving a vehicle. According to this technology, an alcohol detection device (alcohol concentration measurement device) is provided in a vehicle so that an engine start operation is prohibited, for example, unless the alcohol detection device confirms that the driver is free from the influence of alcohol drinking.
The alcohol detection device normally has an alcohol sensor, which measures concentration of alcohol contained in a breath air of the driver, to determine degree of the influence of alcohol drinking.
According to the conventional alcohol detection device, a preparatory operation is performed for a wait period of several tens of seconds before the actual measurement of alcohol to improve the accuracy in measurement of the alcohol sensor. This wait period will necessarily irritate the driver, particularly drivers who have not drunk any alcohol.